ABSTRACT
The animal pole of the fully grown starfish oocyte is recognizable by the eccentric position of the germinal vesicle and, in mature eggs, by the position of the polar bodies formed at the animal pole after germinal vesicle breakdown (Fig. 1) (Shirai and Kanatani, 1980). Fertilized starfish eggs divide equally throughout the cleavage stage. In the first two divisions, the cleavage planes are formed to include the animal-vegetal axis. At the 2<ell stage, when one of the blastomeres is rotated so that its animal-vegetal orientation becomes inverted relative to the other blastomere, two archentera are formed, one by each of the vegetal cytoplasm-derived cells (Fig. 2) (Kuraishi and Osanai, 1988).
